The overall objectives of this proposal are to elucidate the molecular basis for the regional differences in the function of the plasma membrane of mammalian spermatozoa and to determine how the developmental modifications of the sperm membrane which occur during maturation in the epididymis and during capacitation relate to the spermatozon's ability to fertilize an ovum. The structure of the different regions of the sperm plasma membrane is being studied by freeze fracture, negative staining, and thin sectioning. Efforts are being focused to identify changes in the distribution and structure of integral and peripheral membrane proteins during the course of post-testicular sperm development. High resolution electron microscopic investigations and image analysis techniques are being applied to determine the structural mechanisms responsible for the regional differences in sperm membrane structure. Sperm membranes are being isolated into morphologically and chemically distinct subfractions so that the molecular basis of the regional differences in membrane structure can be assessed. The integral and peripheral proteins of the membrane subfractions are being determined by specific extraction protocols, SDS polyacrylamide gel electrophoresis, and correlated electron microscopy. Structural-chemical experiments are also being performed to elucidate the molecular basis for maintaining the ordered arrays of intramembranous particles revealed by freeze fracture. Biochemical changes in the sperm plasma membrane during epididymal maturation are being assessed by biochemical analysis including enzymatic radiolabelling techniques to identify externally oriented surface components. The mechanisms by which the new membrane components appear during the course of epididymal maturation are being investigated.